1. Field of the Invention
This invention relates to a GSM(Group Special Mobile) mobile receiver and has particular reference to the GSM baseband receive architecture of the receiver.
2. Description of the Related Art
In a conventional GSM baseband receiver, analog circuit is used for achieving the various baseband functions. GSM baseband receiver using the analog circuit needs an expensive voltage controlled oscillator, which makes the GSM baseband receiver very costly.
It is an object of the present invention to provide a baseband receiver arrangement for a GSM mobile phone, in which the various baseband functions can be achieved efficiently utilizing as much digital signal processing as possible.
Broadly, the invention resides in a baseband receiver arrangement for a GSM phone comprising in each of two channels for inphase and quadrature components of the received signals, a Sigma-Delta modulator for providing a high frequency single-bit data stream, a first digital filter for converting such data stream to a multi-bit signal at a multiple of the symbol rate, and a second digital filter for converting such multi-bit signal to a multi-bit output signal at the symbol rate.
Preferably, frequency correction is obtained using a complex digital frequency shifter arranged between the first and second digital filters.
Preferably DC offset cancellation is obtained by means of a coarse analog DC offset cancellation section in each channel and a digital DC offset cancellation section operating on the output of the first digital filter of each channel to provide two-stage DC offset cancellation.
Preferably, a digitally controlled analog gain control section is provided in each channel controlled by an RMS signal level calculator deriving its inputs from the output of the first digital filters.
The above and other objects, features and advantages of the present invention will become apparent from the following description with reference to the accompanying drawings which illustrate examples of the present invention.